A novel approach for vanadium precipitation from vanadium-rich stripping solutions: Melamine adsorption and mechanistic insights

As the predominant vanadium recovery method, ammonium salt precipitation generates substantial ammonia nitrogen-containing wastewater. To overcome this limitation, we introduce an innovative vanadium precipitation approach based on melamine as a novel precipitant. Using a vanadium-rich stripping solution as feedstock, we systematically investigated the precipitation performance of melamine for vanadium and the underlying mechanisms. The effects of key parameters such as pH and dosage were examined in simulated solutions. Remarkably, this process achieves a vanadium removal rate of 99.03 % with an exceptional capacity of 1992 mg/g under mild operating conditions. Mechanistic studies indicate that both complexation and redox reactions are involved, while the unique micro–mesoporous structure of melamine synergistically enhances the capture and precipitation of vanadium species. Kinetic and isotherm analyses reveal that the process follows pseudo-second-order kinetics and is best described by monolayer chemisorption. The method was further validated with actual solutions, and response surface methodology was employed to optimize the process conditions. The optimum parameters were identified as pH = 0.86, n(melamine):n(vanadium) = 0.3, temperature = 79 °C, time = 60 min, and stirring speed = 400 rpm, yielding a precipitation rate of 94.12 %. Finally, high-purity vanadium pentoxide (99.15 %) was obtained through staged calcination. This work provides both theoretical insight and technical support for a sustainable vanadium precipitation pathway, with promising environmental and economic benefits.